This invention relates to apparatus for mixing and dispensing multi-component fluids and, more particularly, it concerns foam dispensing guns adapted to be used with resin systems in which two or more fluid components, separately stored in pressurized vessels, are mixed and dispensed as settable foam.
U.S. Pat. Nos. 4,311,254 and 4,398,930 issued to Gary Harding on Jan. 19, 1882 and Aug. 23, 1983, respectively, disclose guns for dispensing for urethane foam in which separate fluid components are fed individually to the gun, passed separately through controlled valve ports and brought into contact with each other only upon reaching a mixing chamber of a nozzle from which the mixed components are discharged as foam. Such foam dispensing guns were developed for use with and have been highly successful commercially in prepackaged foam kits which include two pressurized containers of foam forming chemicals or resins, a dispensing gun and other supplies incidental to use of the kit, such as hoses for attaching the gun to the containers, petroleum jelly for facilitating and assuring sealed connections of couplings, solvent for cleaning gun parts, and a plurality of nozzles adapted for easy replacement in the gun. The resins, commonly referred to as the "A resin" and the "B resin" are supplied separately in the two containers and are typically polymeric isocyanate and polyol amine, respectively. When the two fluid components or resins are mixed, the mixture quickly sets up to form a rigid foam product which is substantially insoluble and extremely difficult, if not impossible, to remove from surfaces with which it comes in contact. Because of these characteristics, the nozzles for the gun are designed to be replaceable and disposable in order to avoid the necessity for cleaning any part of the gun which comes into contact with mixed, as distinguished from separate, foam producing fluid components.
It is important that the nozzles are retained on the gun body with relative rigidity, without leakage of fluid components between the gun body and the nozzle, and yet in a manner to facilitate nozzle removal and replacement. It is equally important that the overall design and construction of the gun body and nozzles meet manufacturing cost criteria consistent with disposal of the gun and all other components of the kit when the supplied foam components are spent. In the guns exemplified by the disclosures of the afore-mentioned patents, the nozzles are mounted on the gun body by telescoping a pair of spaced nozzle ports in the nozzle over a pair of similarly spaced conduit pins projecting from the top of the gun body. A breech component slidable on the gun body between positions of nozzle retention and nozzle release in a direction perpendicular to the conduit pins is formed with camming slots for engagement with diametric pins on the exterior of the nozzle. After the nozzle is placed manually on the conduit pins and the breech is moved forcibly from the position of nozzle release to the position of nozzle retention, the nozzle ports are telescoped forcibly along the length of the conduit pins to its loaded position by coaction of the camming slots on the breech and the diametric pins on the nozzle exterior. A valve control trigger is supported pivotally from the breech to be in an operative relationship with gun body carried valve stems and, when operated to discharge foam from a mounted nozzle, develops a force pulling the breech against the nozzle and the conduit pins. The nozzle cannot, therefore, be released from the gun body during foam dispensing operation of the trigger. Release of the nozzle for removal from the gun body is effected by retraction of the breech and an attendant pivoting of the trigger to an inoperative position away from the valve stems, such movement of the breech causing the cam slots therein to lift the nozzle from the conduit pins.
In the guns described in the above-mentioned patents, the conduit pins over which the nozzle ports are telescoped are precision machined metal (typically brass) parts which are threaded into holes in the gun body which, in turn, is molded from a plastic such as polypropylene. A fluid-tight seal between each nozzle port and each pin is accomplished by an internal circumferential sealing rib in each nozzle port having an effective diameter slightly less than the outside diameter of each pin. The nozzles, and thus the sealing rib in each port, are molded of a relatively strong plastic, such as ABS, so that the sealing ribs of the nozzle ports are stressed firmly and stained into sealing engagement with the machined brass conduit pins on the gun body as the nozzle is forced to its mounted position on the gun body.
Because the conduit pins function to hold the nozzle against movement in reaction to manually forced sliding movement of the breech during nozzle loading and unloading operations and also react to trigger actuating forces, the structural requirements of the conduit pins to withstand the forces to which they are subjected has resulted in small diameter fluid passageways throughout the length of both conduit pins. Early in the commercial development of the guns of the described design, it was recognized that the required relatively small diameter fluid passageways of the conduit pins and the substantial length of those passageways resulted in blockage particularly of the conduit pin through which the "A resin" component or isocyanate was passed. Such blockage was due to the tendency for the isocyanate component to set up or crystalize on contact with air. This problem was solved by adding a solvent flushing port to the "A resin" side of the gun body in accordance with the disclosure of U.S. Pat. No. 4,516,694 issued to Clifford J. Finn on May 14, 1985.
In addition to the conduit pin blockage problem, problems have been encountered more recently with leakage between the conduit pins and the sealing ribs in the plastic nozzle ports. Such leakage is believed to be the result of difficulty in maintaining adequately close dimensional tolerances in machining the exterior cylindrical surfaces of the conduit pins, in the molding of the nozzle port sealing ribs, or in both of these manufacturing procedures. Also the relative incompressibility of the brass pins is believed to have caused fracture points in the plastic ribs in some instances to cause the unwanted leakage. In addition, the manner of mounting the nozzles and the resulting resolution of trigger actuating forces at the nozzle port/conduit pin seals is believed to have contributed to the leakage problem.
While the foam dispensing gun designs represented by the mentioned U.S. patents have proven to be highly effective and commercially successful in a very competitive market, there is need for improvement particularly in the fluid coupling of nozzle/gun passageways and in the arrangement for mounting and removing nozzles from the gun body.